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<h2><a name="SECTION0015120000000000000000">
13.1.2 Data stream format</a>
</h2>

<p>
The data format used by <tt class="module">pickle</tt> is Python-specific.  This has
the advantage that there are no restrictions imposed by external
standards such as XDR<a id='l2h-2453' xml:id='l2h-2453'></a>
(which can't represent pointer sharing); however it means that
non-Python programs may not be able to reconstruct pickled Python
objects.

<p>
By default, the <tt class="module">pickle</tt> data format uses a printable ASCII
representation.  This is slightly more voluminous than a binary
representation.  The big advantage of using printable ASCII (and of
some other characteristics of <tt class="module">pickle</tt>'s representation) is that
for debugging or recovery purposes it is possible for a human to read
the pickled file with a standard text editor.

<p>
There are currently 3 different protocols which can be used for pickling.

<p>

<ul>
<li>Protocol version 0 is the original ASCII protocol and is backwards
compatible with earlier versions of Python.

<p>
</li>
<li>Protocol version 1 is the old binary format which is also compatible
with earlier versions of Python.

<p>
</li>
<li>Protocol version 2 was introduced in Python 2.3.  It provides
much more efficient pickling of new-style classes.

<p>
</li>
</ul>

<p>
Refer to PEP 307 for more information.

<p>
If a <var>protocol</var> is not specified, protocol 0 is used.
If <var>protocol</var> is specified as a negative value
or <tt class="constant">HIGHEST_PROTOCOL</tt>,
the highest protocol version available will be used.

<p>

<span class="versionnote">Changed in version 2.3:
Introduced the <var>protocol</var> parameter.</span>

<p>
A binary format, which is slightly more efficient, can be chosen by
specifying a <var>protocol</var> version &gt;= 1.

<p>

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